1. Field of the Invention
The present invention relates to a centrifugal fan, and more particularly, to a centrifugal fan capable of reducing noise caused due to air blowing.
2. Description of the Related Art
FIG. 17 is a perspective view showing an example of a related-art centrifugal fan. FIG. 18 is a side sectional view showing the example of the related-art centrifugal fan.
As shown in FIGS. 17 and 18, a centrifugal fan 801 includes a casing 810 having an inlet opening 813 (833) and outlet openings 819, and an impeller 830 accommodated in the casing 810. The impeller 830 includes a plurality of blades 851 around a rotary shaft of a motor 860. The centrifugal fan 801 introduces air taken from the inlet opening 813 (833), from a center of the impeller 830 towards between the blades 851 and discharges the air in a radially outward direction of the impeller 830 with a hydrodynamic force generated by a centrifugal action resulting from rotation of the impeller 830. The air which is discharged outwards from an outer periphery of the impeller 830 is then discharged through the outlet openings 819 of the casing 810. Each blade 851 has a vertical end edge portion at a side of the inlet openings 813.
As shown in FIG. 18, the centrifugal fan 801 is thin. The centrifugal fan 801 includes the motor 860 for rotating the impeller 830 at a substantially center part of the casing 810. The motor 860 is an outer rotor brushless motor having a rotor yoke 863 attached to the impeller 830.
The centrifugal fan 801 is widely used for an electrical household appliance, an OA equipment, cooling, ventilation and air conditioning of an industrial equipment, a vehicular blower and the like. The blowing performance and noise of the centrifugal fan 801 are highly influenced by a blade shape of the impeller 830 and a shape of the casing 810 (a structure of the centrifugal fan 801).
In order to reduce the noise and to improve the blowing performance, the shape of the impeller and the structure of the casing have been optimized, and a variety of suggestions have been made.
For example, a centrifugal fan has been suggested which optimizes a blade shape to thereby reduce the noise (for example, refer to JP-A-S63-289295).
In this thin-type centrifugal fan 801, however, the noise is apt to occur. That is, there is a limitation on the thinning of the motor 860 for rotating the impeller 830. Therefore, when the centrifugal fan 801 is made to be thin, a height of the motor 860 becomes relatively larger than that of the centrifugal fan 801. Thus, as shown in FIG. 18, the rotor yoke 863 of the motor 860 protrudes to the center part of the inlet opening 813 (833) of the centrifugal fan 801. The rotor yoke 863 protruding to the inlet opening 813 (833) disturbs flowing of the air from the inlet opening 813 (833) towards the outlet openings 819, so that the noise is generated.